As a high-speed wireless access system using a 5 GHz band, there is the IEEE802.11a standard. In this system, a transmission rate of a maximum of 54 Mbps has been realized using an orthogonal frequency division multiplexing (OFDM) modulation scheme that is technology for stabilizing a characteristic in a multipath fading environment. However, here, the transmission rate is a transmission rate on a physical layer. In fact, since transmission efficiency in a MAC (Medium Access Control) layer is about 50 to 70%, an upper limit value of actual throughput is about 30 Mbps (e.g., see Non-Patent Document 1).
Further, IEEE802.11n is aimed at realizing high-speed communication by using MIMO (Multiple input multiple output) technology capable of realizing spatial multiplexing in the same frequency channel and time using a plurality of antennas, technology using 40 MHz from two current 20 MHz frequency channels, or technology such as frame aggregation in which a plurality of frames are aggregated and then transmitted or improving efficiency through reduction of overhead of a control signal using a block ACK signal, and is capable of realizing a transmission rate of a maximum of 600 Mbps.
Further, IEEE802.11ac that is currently being developed is aimed at realizing faster wireless communication than IEEE802.11n by using communication technology using 80 MHz from simultaneous use of four 20 MHz frequency channels or MU-MIMO (Multi-User MIMO) technology in which communication with a plurality of wireless stations is performed in the same frequency channel at the same time (e.g., see Non-Patent Document 2).
In recent years, as the demand for large capacity wireless communication has rapidly increased, base stations of wireless LANs have been installed at several places such as homes or stations. However, in an environment in which communication cells (each including one base station and a plurality of terminal stations) using the same frequency channel are adjacent, signals interfere with each other, and excellent wireless communication cannot be performed (in general, in a wireless communication system such as a mobile phone or a wireless LAN, one wireless base station, or a communication cell including a base station and a plurality of terminal stations is regarded as a minimum unit of a wireless network).
In order to resolve such a problem, in wireless communication in a current wireless LAN, a different frequency channel or a different time is allocated to each communication cell to avoid interference and then wireless communication is performed. However, even when adjacent communication cells increase, since radio resources (frequency channel or time) allocated to each communication cell are finite, sufficient radio resources are not allocated to each communication cell and a transmission rate is degraded. Further, as standardization progresses in order of IEEE802.11a, IEEE802.11n, and IEEE802.11ac, when a 20 MHz OFDM block is used as one frequency channel, the number of frequency channels that can be simultaneously used is reduced to 4, 2, and 1, and thus, frequency channels that can be allocated are reduced. Accordingly, adjacent communication cells that perform communication using the same frequency channel increase.
Further, in the Radio Act, since the number of frequency channels that can be used in the wireless LAN is limited, when there are many adjacent communication cells, communication is performed using the same frequency channel as an adjacent channel. In this environment, a throughput is degraded due to interference from an adjacent communication cell. In order to avoid this interference, frequency channel allocation technology is used in which a frequency channel used by the adjacent communication cell is sensed and wireless communication is performed using an unused frequency channel. Further, when a communication frame is not received due to the interference from the adjacent communication cell, the same communication frame is transmitted again. Data transmission is performed through retransmission until the communication frame is received.
In order to resolve this problem, technology for increasing a transmission rate of each communication cell by allowing respective communication cells to simultaneously perform communication even when the communication cells are adjacent by suppressing an interference power directed to an adjacent communication cell in advance through control of a transmission power has been considered (e.g., see Non-Patent Document 3).
Further, in order to increase a transmission rate of each communication cell, interference suppression using MIMO technology in which interference suppression is performed by controlling directivity of a transmitted radio wave using propagation channels between a plurality of antennas for transmission and reception giving interference has been considered.